1. Technical Field
The invention relates to an image forming apparatus, an image reading apparatus and a complex machine provided with these.
2. Related Art
There have been known complex machines, each of which includes a print function, a copy function and a facsimile function. In a complex machine disclosed in JP-A-2000-270134 for example, a singly usable scanner is added to a singly usable printer later on so as to be usable as a copier or a facsimile machine. On the other hand, such an apparatus including a printer, a scanner, and a complex machine has built-in electrical circuits for obtaining power from an external commercial power supply and supplying the power to respective parts of the apparatus. An apparatus disclosed in JP-A-2003-54097, for example, includes, as the electrical circuits, a rectifying circuit for rectifying an alternating-current input from an external commercial power supply, and a low-voltage power supply circuit such as a DC-DC converter for generating low voltages from the power rectified by the rectifying circuit for the power supply to the respective parts of the apparatus.
By the way, the constructions of the electric circuits need to be sufficiently studied in order to make a printer and a scanner singly usable and also usable as a complex machine by connecting them with each other like those disclosed in JP-A-2000-270134. Specifically, the rectifying circuit is an essential circuit for each, in the case of using each of the printer and the scanner singly for example, whereas one rectifying circuit can be shared in the case of using them as a complex machine by connecting them with each other. In this case, a construction for making the rectifying circuit commonly usable needs to be prepared. Further, if special electric circuits are provided for the single use and for the use as the complex machine in each of the printer and the scanner, labor hour and cost for circuit design increase. Hence, it is preferable that the electric circuits are maximally shared. Furthermore, when one rectifying circuit is shared and power is supplied to the respective parts of the both apparatuses by generating low voltages from the rectified power in the complex machine, power consumption at low voltages increases as a whole. Accordingly, an input current from the external commercial power supply becomes excessive when loads have low power factors. This is not preferable in light of the durability of the parts and power consumption efficiency. However, no consideration is made on these points in the above machine and apparatus disclosed in JP-A-2000-270134 and JP-A-2003-54097.